I learned through YouTube tutorials. Find a popular free virtual synth, I'd recommend Synth1. (Popular because you want lots of content available) and try to understand the very basics of the pieces of it.
Once you've got that down, most popular synthesizers use a very similar "subtractive" architecture, so once you understand the basics of your chosen one, it's simple to follow tutorials using other synthesizers. From there I'd recommend finding a youtuber you like learning from even if they don't use the same synth as you.
Once you've got that down, most popular synthesizers use a very similar "subtractive" architecture, so once you understand the basics of your chosen one, it's simple to follow tutorials using other synthesizers. From there I'd recommend finding a youtuber you like learning from even if they don't use the same synth as you.